The film follows David Lightman (Broderick), a young hacker who unwittingly accesses WOPR (War Operation Plan Response), a United States military supercomputer programmed to predict possible outcomes of nuclear war. Lightman gets WOPR to run a nuclear war simulation, originally believing it to be a computer game. The simulation causes a national nuclear missile scare and nearly starts World War III.

The film was a box office success, costing US$12 million, and grossing $79,567,667 after five months in the United States and Canada. The film was nominated for three Academy Awards. A sequel, WarGames: The Dead Code, was released direct to DVD on July 29, 2008.

David Lightman (Matthew Broderick) is a bright but unmotivated Seattle high school student and hacker. After receiving a failing grade in school, he uses his IMSAI 8080microcomputer to hack into the district's computer system. He then changes his grade and does the same for his friend and classmate Jennifer Mack (Ally Sheedy). Later, while dialing every number in Sunnyvale, California to find a set of forthcoming computer games, a computer that does not identify itself intrigues David. On the computer he finds a list of games, starting with general strategy games like chess, checkers, backgammon, and poker and then progressing to titles like "TheaterwideBiotoxic and Chemical Warfare" and "Global Thermonuclear War", but cannot proceed further. Two of his hacker friends explain the concept of a backdoor password and suggest tracking down the Falken referenced in "Falken's Maze", the first game listed. David discovers that Stephen Falken is an early artificial intelligence researcher, and guesses correctly that his dead son's name "Joshua" is the backdoor password.

David does not know that the Sunnyvale phone number connects to WOPR, or "Joshua", at Cheyenne Mountain. He starts a game of Global Thermonuclear War, playing as the Soviet Union. The computer starts a simulation that briefly convinces the military personnel at NORAD that actual Soviet nuclear missiles are inbound. While they defuse the situation, Joshua nonetheless continues the simulation to trigger the scenario and win the game. It continuously feeds false data such as Soviet bomber incursions and submarine deployments to the humans at NORAD, pushing them into raising the DEFCON level and toward a retaliation that will start World War III. David learns the true nature of his actions from a news broadcast, and the FBI arrests him and takes him to NORAD. He realizes that Joshua is behind the NORAD alerts but fails to convince McKittrick and faces imprisonment. David escapes NORAD by joining a tourist group and, with Jennifer's help, travels to the Oregon island where the widowed Falken (John Wood) now lives. David and Jennifer find that Falken has become despondent and believes that nuclear war is inevitable. The teenagers convince Falken that he should return to NORAD to stop Joshua.

The computer stages a massive Soviet first strike with hundreds of missiles, submarines, and bombers. Believing the attack to be genuine, NORAD prepares to retaliate. Falken, David, and Jennifer convince military officials to cancel the second strike and ride out the non-existent attack. Joshua tries to launch the missiles itself, however, using a brute force attack to obtain the launch code. Without humans in the silos as a safeguard, the computer will trigger a mass launch. All attempts to log in and order Joshua to cancel the countdown fail, and all weapons will launch if the computer is disabled. Instead, Falken and David direct the computer to play tic-tac-toe against itself. This results in a long string of draws, forcing the computer to learn the concept of futility. Joshua obtains the missile code but before launching, it cycles through all the nuclear war scenarios it has devised, finding they too all result in stalemates. Having discovered the concept of Mutually Assured Destruction ("WINNER: NONE"), the computer concludes that nuclear warfare is "a strange game" in which "the only winning move is not to play." Joshua then offers to play "a nice game of chess", and relinquishes control of NORAD and the missiles.

Development on WarGames began in 1979, when writers Walter F. Parkes and Lawrence Lasker developed an idea for a script called The Genius, about "a dying scientist and the only person in the world who understands him – a rebellious kid who's too smart for his own good." Lasker was inspired by a television special presented by Peter Ustinov on several geniuses including Stephen Hawking. Lasker said "I found the predicament Hawking was in fascinating – that he might one day figure out the unified field theory and not be able to tell anyone, because of his progressive ALS. So there was this idea that he'd need a successor. And who would that be? Maybe this kid, a juvenile delinquent whose problem was that nobody realized he was too smart for his environment." The concept of computers and hacking as part of the film was not yet present.[1]

The Genius began its transformation into WarGames when Parkes and Lasker met Peter Schwartz from the Stanford Research Institute. "There was a new subculture of extremely bright kids developing into what would become known as hackers," said Schwartz. Schwartz made the connection between youth, computers, gaming, and the military. Parkes and Lasker came up with several different military-themed plotlines prior to the final story. One version of the script had an early version of WOPR named "Uncle Ollie", or OLI (Omnipresent Laser Interceptor), a space-based defensive laser run by an intelligent program, but this idea was discarded because it was too speculative.[1] Director John Badham coined the name "WOPR", feeling that the name of NORAD's SIOP (Single Integrated Operational Plan) was "boring, and told you nothing".[2] The name "WOPR" played off of the Whopper hamburger, and a general sense of something going "whop".[2]

David Lightman was modeled on David Scott Lewis, a hacking enthusiast Parkes and Lasker met.[1][3] Falken was inspired by Stephen Hawking with the appearance of John Lennon, who was interested in the role. General Beringer was based on James V. Hartinger, the then-commander-in-chief of NORAD who Parkes and Lasker met while visiting the base, and who, like Beringer, favored keeping humans in the decision loop.[1]

Martin Brest was originally hired as director but was fired after 12 days of shooting because of a disagreement with the producers,[6] and replaced with John Badham. Several of the scenes shot by Brest remain in the final film. Badham said that "[Brest had] taken a somewhat dark approach to the story and the way it was shot. It was like [Broderick and Sheedy] were doing some Nazi undercover thing. So it was my job to make it seem like they were having fun, and that it was exciting." According to Badham, Broderick and Sheedy were "stiff as boards" when they came onto the sound stage, having both Brest's dark vision and the idea that they would soon be fired. Badham did 12–14 takes of the first shot to loosen the actors up. At one point, Badham decided to have a race with the two actors around the sound stage with the one who came last having to sing a song to the crew. Badham lost and sang "The Happy Wanderer", the silliest song he could think of.[7]

Tom Mankiewicz says he wrote some additional scenes during shooting which were used.[8]

WarGames did well at the North American box office, earning $79,567,667, the fifth-highest of 1983.[1][9] The film was screened out of competition at the 1983 Cannes Film Festival.[10]President Reagan, a family friend of Lasker, watched the film and discussed the plot with members of Congress.[1]

The film received critical acclaim. Film review aggregator Rotten Tomatoes reported that 92% of sampled critics gave the film positive reviews and that it got a rating average of 7.5 out of 10.[11] Film critic Roger Ebert gave the film four out of four stars, calling it "an amazingly entertaining thriller" and "one of the best films so far this year", with a "wonderful" ending.[12]Softline praised the film as being "completely original"; unlike other computer-related films like Tron that "could (and do) exist in substantially the same form with some other plot", WarGames "could not exist if the microcomputer did not exist ... It takes the micro and telecommunications as a given—part of the middle-class American landscape". The magazine praised the film as "Very funny, excruciatingly suspenseful, and endlessly inventive, this movie is right on the mark; authentic even when highly improbable".[13]Computer Gaming World stated that "Wargames is plausible enough to intrigue and terrifying enough to excite ... [it] makes one think, as well as feel, all the way", raised several moral questions about technology and society, and recommended the film to "Computer hobbyists of all kinds".[14]

Bulletin Board System operators reported an unusual rise in activity in 1984, which at least one sysop attributed to WarGames introducing viewers to modems.[16] The scenes showing Lightman's computer dialing every number in Sunnyvale led to the term "war dialing" (earlier known as "demon dialing"), a technique of using a modem to scan a list of telephone numbers to search for unknown computers, and indirectly to the newer term "wardriving".[17]

The film's music was composed and conducted by Arthur B. Rubinstein. A soundtrack album including songs (recorded for but not used in the film) and dialogue excerpts was released by Polydor. Intrada Records issued an expanded release in 2008 with the complete score, without the dialogue.

The folk rock supergroup Crosby, Stills & Nash were tapped at one point to write a title song for the film, but at the last minute it was scrapped from the project. The band released the song anyway, with a video made of footage from the movie airing on MTV. It was available on their now out-of-print album Allies.

In November 2006, pre-production began on a sequel, titled WarGames: The Dead Code. It was directed by Stuart Gillard, and starred Matt Lanter as a hacker named Will Farmer facing off with a government supercomputer called RIPLEY.[21] MGM released the sequel directly to DVD on July 29, 2008 along with the 25th Anniversary Edition DVD of WarGames. To promote the sequel, the film returned to selected theaters as a one-night-only twenty-fifth anniversary event on July 24, 2008.[22]

There have been various rumours of reboots. It was reported in February 2009 that Leonardo DiCaprio was looking to produce one,[23] and in 2011 MGM Studios were said to be planning a reboot with Seth Gordon signed on to direct, although no writers or cast were yet on board.[24]